While the background of the present invention is discussed in terms of plasma display panel (PDP) applications, it is sunderstood that the present invention is useful in flat panel display applications, in general.
The PDP typically comprises a pair of forward and backward insulation substrates arranged in opposition to each other to form a plurality of cells as display elements each defined by the insulation substrates supported with a constant interval and cell barriers arranged between the insulation substrates, two crossing electrodes disposed on internal surfaces of the insulation substrates with a dielectric layer interposed between the electrodes which cause electric discharge in a plurality of cells by application of an alternating current. Due to this application of alternating current, phosphor screens formed on the wall surface of the cell barrier emit light and display images which are passed through the transparent insulation substrate (typically called the front glass substrate or plate).
One area of concern for PDP manufacturers is display contrast, which affects the ultimate picture viewed by the consumer. To improve the display contrast, it is essential to decrease the reflection of external light from the electrodes and conductors arranged on the front glass substrate of the PDP device. This reflection decrease can be accomplished by making the electrodes and conductors black as viewed through the front plate of the display.
Furthermore, another area of concern for PDP manufacturers is environmental in nature and is the lead and cadmium contained in the prior art black conductor compositions and black electrodes of the PDP device. It is desirable to reduce and/or eliminate the lead and cadmium contained in the black conductor compositions and electrodes while still maintaining the required physical and electrical properties of the compositions and electrodes.
For example, in Japanese Kokai Patent No. HEI 10[1998]-73233 and its division Japanese Kokai Patent No. 2004-158456, light-forming black electrode compositions containing conductive particles consisting of at least one substance chosen from ruthenium oxide, ruthenium polyoxide, or their mixture and an inorganic binder, black electrodes using such compositions, plasma display panels using such black electrodes, and a method for making such a plasma display panel are disclosed. These literature references are not directed to lead-free black conductive compositions. In these references, there are no descriptions of lead-free black conductive compositions in terms of properties such as the appearance and strength of black electrodes obtained by sintering the compositions, electrical properties such as resistance, and a balance of all the properties for PDP electrodes.
Japanese Patent No. 3510761 discloses alkali-developable photocurable conductive paste compositions for plasma display panels, easily forming high-precision electrode circuits on large areas by photolithography and firing below 600° C. Such compositions contain (A) copolymer resins obtained by the addition of glycidyl acrylate and/or glycidyl methacrylate to copolymers of methyl methacrylate and methacrylic acid and/or acrylic acid; (B) photochemical polymerization initiator; (C) photopolymerizable monomer; (D) at least one conductive metal powder selected from Au, Ag, Ni, and Al; (E) glass frit; and (F) a phosphoric acid compound. In this literature, a low-melting glass frit is described using lead oxide as the preferred main component, while there are no descriptions of lead-free conductive compositions, especially black conductive compositions.
Japanese Patent No. 3541125 discloses alkali-developable curable conductive paste compositions that have adhesion to the substrate after being fired, with adhesion between layers, suppression of curling, easy formation of high-precision conductive circuit patterns in large areas by photolithography, and are especially useful for forming underlayer electrode circuits of bus electrodes formed on the front substrate of plasma display panel. These compositions consist of: (A) carboxy-group-containing resins; (B) photopolymerizable monomer; (C) photochemical polymerization initiator; (D) silanol-group-containing synthetic amorphous silica fine powder; (E) conductive powder; and if needed (F) heat-resistant black pigment; (G) glass frit; and (H) stabilizer. In particular, this literature has a description of a low-melting glass frit using lead oxide as the preferred main component, while there are no descriptions of lead-free conductive compositions, especially black conductive compositions.
Japanese Patent No. 3479463 discloses photocurable conductive compositions providing adhesion on a substrate in steps involving drying, exposure, development and firing, and resolution, satisfying the need for both a sufficient conductivity and blackness after being fired and discloses plasma display panels (PDP) with formation of the underlayer (black layer) electrode circuit using such compositions. The basic first embodiment of the compositions described in this literature contains (A) black conductive microparticles having a surface area to weight ratio larger than 20 m2/g and containing at least one substance chosen from ruthenium oxide or other ruthenium compound, copper-chromium black composite oxide and copper-iron black composite oxide, (B) an organic binder, (C) a photopolymerizable monomer, and (D) a photochemical polymerization initiator. The second embodiment contains (E) inorganic fine particles in addition to the above components. In this literature, with respect to this composition, the inorganic fine particles (E) contain, as needed, glass powder with a softening point of 400-600° C., conductive powder, heat-resistant black pigment, silica powder, etc. However, in the compositions of this literature, glass powder is not an essential component, and even when a glass component is added, lead oxide is described as the preferred main component, with no disclosure of lead-free black conductive compositions.
Japanese Patent No. 3538387 discloses photocurable conductive compositions having storage stability, providing adhesion on substrates in the different steps of drying, exposure, development and firing, and resolution, and satisfying the need for both sufficient blackness after being fired, and discloses plasma display panels (PDP) with the formation of the underlayer (black layer) electrode circuit using such compositions. The basic first embodiment of these photocurable resin compositions contains (A) tricobalt tetroxide (Co3O4) black microparticles, (B) organic binder, (C) photopolymerizable monomer, and (D) photochemical polymerization initiator. The second embodiment contains (E) inorganic microparticles in addition to the above components. In this literature, with respect to this composition, the inorganic fine particles (E) contain, as needed, a glass powder with a softening point of 400-600° C., conductive powder, heat-resistant black pigment, silica powder, etc. However, the compositions do not contain conductive materials such as ruthenium oxide, and glass powder is not an essential component. Even when a glass component is added, lead oxide is described as the preferred main component, with no disclosure of lead-free black conductive compositions.
Japanese Patent No. 3538408 discloses photocurable conductive compositions having storage stability, providing adhesion on substrates in different steps of drying, exposure, development and firing, and resolution, and satisfying the need for both sufficient conductivity and blackness after being fired, and discloses plasma display panels (PDP) with the formation of the underlayer (black layer) electrode circuit using such compositions. The basic first embodiment of these photocurable resin compositions contains (A) black inorganic microparticles such as inorganic binder-coated ruthenium oxide or another ruthenium compound, copper-chromium black composite oxide, copper-iron black composite oxide, cobalt oxide, etc., (B) organic binder, (C) photopolymerizable monomer, and (D) photochemical polymerization initiator. The photocurable compositions described in this literature are characterized by containing inorganic binder-coated black inorganic microparticles (A). The inorganic binder-coated black inorganic microparticles (A) are obtained by pulverizing molten materials of inorganic microparticles and an inorganic binder, with an inorganic binder having a softening point of 400-600° C. and glass powder with lead oxide as the main component being described as preferred, but with no disclosure of lead-free black conductive compositions.